Does Higher T1 Slope Predict Poor Outcomes Following Posterior Cervical Fusion for Degenerative Pathology?

Abstract

While T1 slope is an important parameter in cervical deformity surgery, its importance in posterior cervical fusion (PCF) remains unknown. Among patients undergoing degenerative PCF, we evaluated the impact of T1 slope on: 1) mechanical complications, 2) reoperation, and 3) patient-reported outcomes measures (PROMs). A retrospective, cohort (2010-22) of patients undergoing elective PCF for degenerative pathology was analyzed as: 1) entire sample, 2) isolated cervical fusions, and 3) cervicothoracic fusions. Primary exposure was postoperative T1 slope (angle between superior T1 endplate and horizontal). Outcomes included mechanical complications, reoperation, and PROMs. Multivariable logistic regression controlled for age, body mass index and preoperative PROM. Among 234 PCF patients (age: 63 ± 10 years; 53% male), the mean postoperative T1 slope was 28 ± 10°. Mechanical complications occurred in 41 patients (18%), and 14 (6%) required reoperation. In the overall cohort, mechanical complications (30 ± 8 vs. 28 ± 10°, P = 0.239) and reoperation (27 ± 8 vs. 28 ± 10°, P = 0.714) had no association with T1 slope. Negative correlation with 12-month NDI% (ρ = -0.15, P = 0.041), lost significance on multivariable analysis (β = -0.15, 95% CI = -0.38-0.07, P = 0.177). Isolated cervical fusions (23%): mechanical complications, reoperation, and PROMs had no association with T1 slope. Cervicothoracic fusions (77%): mechanical complications were associated with a greater T1 slope (31 ± 8 vs. 27 ± 8°, P = 0.039; OR=1.05, 95% CI=1.00-1.10, P = 0.040), while no significant association was found with reoperation (29 ± 8 vs. 28 ± 9°, P = 0.747). Negative correlation with 12-month NDI% (ρ = -0.19, P = 0.027), lost significance on multivariable analysis (β = -0.22, 95% CI: -0.56-0.11, P = 0.182). In patients undergoing degenerative PCF, higher T1 slope was associated with increased mechanical complications in cervicothoracic fusions but not isolated cervical fusions. T1 slope warrants further study in degenerative cervical fusions.